1. Field of the Invention
The invention relates to the field of tubular joints used, in particular, in wells, such as hydrocarbon wells and geothermal wells.
2. Description of Related Art
These joints are generally used to connect great length tubes together or to connect great length tubes and sleeves together, to allow casing or tubing strings to be formed.
Moreover, these joints must be able to withstand considerable bending, tensile, compressive and sometimes torsional stresses, and also considerable pressure variations between the interior and the exterior. Furthermore, these joints must also in some cases be gas-tight. For these reasons, the joints are often of the threaded type and the sleeves and tubes are generally made from steel or from an alloy having a high yield point (possibly obtained by heat treatment). In the case of threaded joints, gas-tightness is most often provided by sealing surfaces with interfering “metal-on-metal” type contact.
In order to reduce the initial overall size of the tubes and also possibly to allow the drilling of wells having a uniform diameter, it has been proposed, in particular in documents U.S. Pat. No. 6,604,763 and WO 03/071086, forcefully to expand them diametrally in situ by means of an expansion tool known as a “ball”. Sealed threaded joints such as, for example, those described in document EP 0488912, are able to withstand such expansion but lose their sealing characteristics during the expansion, the nose at the end of the male element, which carries a male sealing surface, falling toward the axis during the expansion (“banana” effect), and this breaks the seal.
In order to solve this problem, the Applicant proposed, in document WO 02/01102, a threaded tubular joint, the male nose of which is provided at one end with an annular finger fitted in a female groove, the groove providing support for the finger and preventing the male finger from falling toward the axis during the expansion.
However, a threaded joint of this type does not have sufficiently high sealing characteristics when the expansion rate is greater than 10%. The deformations generated by the expansion ball displace, or even eliminate, the contacts between the male finger and the groove and this displaces the interference contacts between sealing surfaces by reducing or even eliminating them.
The term “interference contact” refers, in the present context, to a contact developing a contact pressure between two contacting surfaces. The higher the contact pressure, the higher the fluid pressure the joint is able to withstand without the seal being broken. In addition to the fluid pressure, which may be exerted inside or outside the threaded joint, axial tensile or compressive loads may modify the contact pressure and therefore the sealing characteristics. In other words, owing to the embodiment of these joints, their seal may not be identical with respect to the internal pressure or the external pressure, nor be stable as a function of the load.
In order to improve the situation, the Applicant proposed, in patent document FR 02/03842 (filed on 27 Mar. 2002 under the internal priority of patent document FR 02/00055, filed on 3 Jan. 2002), a metal/metal tubular sealing joint provided with an annular finger (or lip) described in document WO 02/01102 and having inclined male and female shoulders, highly tightened against one another after expansion, the shoulder on the female element consisting of the flank of a groove and the shoulder on the male element being able to pre-exist or result from the pressing of the male element at the bottom of the groove during the expansion.
This joint was configured to provide a seal at high expansion rates, typically greater than 10%, but its sealing characteristics may prove insufficient if the sealing characteristics required in the various forms of loading are high.